Angular Unconformities

All unconformities represent a gap in time when no sediment was deposited.

May be a result of change in environment or earths movements.

Occur where the rocks above the unconformity have a different dip or strike to the rocks below the plane of unconformity.

• Stage 1: Depostion of beds of rock, with the oldest at the bottom and the youngest at the top.
• Stage 2: Beds of rock are tilted by earths movements as a result of compressive forces folding the rocks.
• Stage 3: Erosion of the older beds of rock, this could be a gap of thousands or millions of years.
• Stage 4: Depostion of younger overlying beds of rock. They are deposited uncomformably on the underlying beds. The eroded surface is the plane of unconformity. Fragements of the underlying rocks may form conglomerate, a sedimentary rock formed of pebbles.
• Stage 5: Upflit and erosion, expose the unconformity. All the rocks will be folded again so the younger rocks will also be tilted.

• There is a difference in stike and dip of the beds above and below the plane of unconformity.
• There is a presence of basal conglomerate.
•  Older beds and structures are cut off by overlying younger rocks above the plane of unconformity.
• Rocks above the unconformity are younger than the rocks below the unconformity.